Month: September 2016

My Night Sky Observing at the Worldcon in Kansas City was rained out. I hope some of you had clear skies and observed Saturn, Mars, and Antares aligned in Scorpio (which is now a triangle), and used my Animated Moon Map to find the Apollo sites.

This month the autumnal equinox falls on September 22, and that got me wondering about what season it is on Mars, and what I might take people to see if I did a Night Sky program there. My brain liked this exercise, so I thought I’d share this “snack” with you.

An equinox is when the sun’s path crosses a planet’s equatorial plane. On the equinox, day and night are equal lengths. Like Earth, Mars is “tipped” on its axis, so it too has equinoxes. But because the north pole of Mars points to a different part of the sky, and the inclination is 25 (versus Earth’s 23.5) degrees, the constellations we associate with spring and fall equinoxes are different on Mars.

Polaris is our north star because it is “above” the spin axis of Earth. All the other stars (and their constellations) appear to rotate around it in a big circle every 24 hours.

The Martian north pole points to a spot without any bright star about 28 degrees from Polaris in the direction of Capricorn (RA 20.5 hours). This pole is about halfway between Alderamin in Cepheus and Deneb in Cygnus a.k.a. the Northern Cross. (Reference: Byrd, Deborah, “Does Mars have a North Star,” EarthSky, 6-16-16) Since Cepheus and Cygnus are on opposite sides of the pole, and rotate around it every Martian sol (24 hours 39 minutes), they can be used to tell time and month on Mars like the Big Dipper and Cassiopeia on Earth.

Mars does not have a pole star. But Deneb and Sadr in constellation Cygnus, can be used as “pointer” stars to locate the pole in the direction of Alderamin in Cepheus. The constellations Cepheus and Cygnus rotate around the pole and can be used like a clock to tell time. (Image by Tomruen via Wikimedia Commons with labels modified by Marianne Dyson)

Equinoxes occur twice a year as the sun passes north (spring), then south (fall), of the equator. On Mars they are the first sol of Months 1 and 7 of a 12-month year where a month is the time it takes Mars to pass through 30 degrees of its orbit. Because the orbit is elliptical, instead of each month being 56 sols (668 sols /year divided by 12), the northern fall and winter months average 50 days and the spring and summer months last about 62 days.

The months of fall (gray) and winter (red) are shorter than the months of spring (green) and summer (orange) because Mars moves faster at perihelion than aphelion. (Image from Kuuke’s Strerrenbeelden.)

The Martian fall equinox was July 4, 2016. Fall lasts until the winter solstice which is November 28 on Mars and December 21 on Earth. So this October, it will be fall on both Earth and Mars. We will be admiring Cassiopeia (the “W”) and Cepheus to the north, Cygnus overhead, and Perseus (the square) to the south.

For the Martians, the sun is moving toward Leo and then into Virgo at their winter solstice. Cassiopeia and Cygnus are high up for them, too. But because their pole is shifted toward Capricorn, they also have a good view of the Sagittarius teapot and should also see some of Earth’s southern hemisphere constellations, Indus and Piscus Austrinus.

Like us, Martians will see Venus as an evening star in October, while Earth and the Moon will be visible in the morning. And the Milky Way should be spectacular without any light pollution or buildings to spoil the view. It will also look different because the atmosphere of Mars is too thin to make stars twinkle.

If we had the Worldcon on Mars, we’d never have to cancel because of rain. I’ll volunteer to do Night Sky Observing, and then lead a discussion about why we should build a Martian Stonehenge to help us view the vernal equinox in Mars Year 42 (Earth date 5-22-32). I hope you’ll join me!

Writing about Space

I’m teaching short story writing in an after-school enrichment program at St. Thomas the Apostle school in Nassau Bay (across from JSC) that may be expanded to include members of the community if there is interest. If your student in 4th grade and up likes creating stories, and would like a published mentor to help them develop their skills, please call the St. Thomas and ask for the Director of Enrichment.

I offer technical and content editing for adult writers, as well as workshops for groups of five or more on writing memoirs and publishing them. See my Resources for Writers page for more information.